Chemotactic Cytokine Receptor 1 (CCR1) belongs to a large family (>20) of chemotactic cytokine (chemokine) receptors that interact with specific chemokines (>50) to mediate leukocyte trafficking, granule exocytosis, gene transcription, mitogenic effects and apoptosis. Chemokines are best known for their ability to mediate basal and inflammatory leukocyte trafficking. The binding of at least three chemokines (MIP-1 alpha/CCL3, MCP3/CCL7 and RANTES/CCL5) to CCR1 is responsible for the trafficking of monocytes, macrophages and TH1 cells to inflamed tissues of rheumatoid arthritis (RA) and multiple sclerosis (MS) patients (Trebst et al. (2001) American J of Pathology 159 p. 1701). Macrophage inflammatory protein 1 alpha (MIP-1 alpha), macrophage chemoattractant protein 3 (MCP-3) and regulated on activation, normal T-cell expressed and secreted (RANTES) are all found in the CNS of MS patients, while MIP-1 alpha and RANTES are found in the CNS in the experimental autoimmune encephalomyelitis (EAE) model of MS (Review: Gerard and Rollins (2001) Nature Immunology). Macrophages and Th1 cells in the inflamed synovia of RA patients are also major producers of MIP-1 alpha and RANTES, which continuously recruit leukocytes to the synovial tissues of RA patients to propagate chronic inflammation (Volin et al. (1998) Clin. Immunol. Immunopathology; Koch et al. (1994) J. Clin. Investigation; Conlon et al. (1995) Eur. J. Immunology). Antagonizing the interactions between CCR1 and its chemokine ligands is hypothesized to block chemotaxis of monocytes, macrophages and Th1 cells to inflamed tissues and thereby ameliorate the chronic inflammation associated with autoimmune diseases such as RA and MS.
Evidence for the role of CCR1 in the development and progression of chronic inflammation associated with experimental autoimmune encephalitis (EAE), a model of multiple sclerosis, is based on both genetic deletion and small molecule antagonists of CCR1. CCR1 deficient mice were shown to exhibit reduced susceptibility (55% vs. 100%) and reduced severity (1.2 vs. 2.5) of active EAE (Rottman et al. (2000) Eur. J. Immunology). Furthermore, administration of small molecule antagonist of CCR1, with moderate affinity (Ki=120 nM) for rat CCR1, was shown to delay the onset and reduce the severity of EAE when administered intravenously (Liang et al. (2000) J. Biol. Chemistry). Treatment of mice with antibodies specific for the CCR1 ligand MIP-1 alpha have also been shown to be effective in preventing development of acute and relapsing EAE by reducing the numbers of T cells and macrophages recruited to the CNS (Karpus et al. (1995) J. Immunology; Karpus and Kennedy (1997) J. Leukocyte Biology). Thus, at least one CCR1 ligand has been demonstrated to recruit leukocytes to the CNS and propagate chronic inflammation in EAE, providing further in vivo validation for the role of CCR1 in EAE and MS.
In vivo validation of CCR1 in the development and propagation of chronic inflammation associated with RA is also significant. For example, administration of a CCR1 antagonist in the collagen induced arthritis model (CIA) in DBA/1 mice has been shown to be effective in reducing synovial inflammation and joint destruction (Plater-Zyberk et al. (1997) Immunology Letters). Another recent publication described potent antagonists of murine CCR1 that reduced severity (58%) in LPS-accelerated collagen-induced arthritis (CIA), when administered orally (Biorganic and Medicinal Chemistry Letters (15 (2005) 5160-5164). Published results from a Phase I clinical trial with an oral CCR1 antagonist demonstrated a trend toward clinical improvement in the absence of adverse side effects (Haringman et al. (2003) Ann Rheum. Dis.). One third of the patients achieved a 20% improvement in rheumatoid arthritis signs and symptoms (ACR20) on day 18 and CCR1 positive cells were reduced by 70% in the synovia of the treated patients, with significant reduction in specific cell types including 50% reduction in CD4+ T cells, 50% reduction in CD8+ T cells and 34% reduction in macrophages.
Studies such as those cited above support a role for CCR1 in MS and RA and provide a therapeutic rationale for the development of CCR1 antagonists.